Most cases of male infertility cannot be adequately explained although some are thought to involve fertilization dysfunction. The objective of this project is to understand the cell and molecular biology of one of the first stages of the human fertilization process - the early association of the sperm with the egg's zona pellucida - and to determine if there is a class of male infertility resulting from dysfunction of this stage of gamete interaction. The proposed experiments will test with human gametes a model developed from animal studies which suggests sperm-zona binding is due to bonds formed between an externally exposed, plasma membrane sperm enzyme (galactosyltransferase) and terminal N-acetylglucosamine residues in the zona pellucida. In pilot experiments, we have detected galactosyltransferase on human sperm. In this project we will test the role of this enzyme in the binding of sperm to the human zona pellucida by determining: 1) the effectiveness of inhibitors of the enzyme in blocking sperm-zona binding, 2) the ability of the human zona pellucida to serve as an acceptor for sperm galactosyltransferase-catalyzed transfer of (3H)-galactose from uridinediphospho(3H)galactose and 3) the ability of uridinediphosphogalactose to cause detachment of sperm bound to the human zona pellucida. The incidence of subnormal sperm-zona binding in infertile men will be reinvestigated using an assay of increased precision, and the correlation between the sperm-zona binding and sperm galactosyltransferase activity will be determined in both fertile and infertile men, to see if subnormal sperm transferase activity can be used as an indicator of infertility. Finally, the major protein components of the human zona pellucida will be analyzed by SDS/polyacrylamide gel electrophoresis. A solubilized preparation of human zonae pellucidae will be tested for its ability to induce acrosome reactions in human sperm and to see if it contains material with properties expected of a sperm receptor.